There is a conventional technology that determines the wakefulness level of a subject by using biometric information on the subject so that there is no burden placed on the subject. By using this technology in vehicles, it is possible, for example, to determine the wakefulness level of a driver and to report any danger.
There is a technology, for example, that uses the maximum frequency and the maximum spectral density, both calculated from a subject's heartbeat signal, to determine the wakefulness level of the subject. With this technology, a scale is previously set that is the range over which the maximum frequency and the maximum spectral density vary between when a subject is fully awake and when a subject is not fully awake, i.e., from the state in which a subject feels no drowsiness to the state in which the subject feels drowsy. The maximum frequency and the maximum spectral density are calculated every time the subject's heartbeat signal is obtained and the obtained values are applied to the scale, thereby determining the wakefulness level of the subject in real time.
Furthermore, there is a technology, for example, that uses the heart rate and the blood pressure obtained when a subject is fully awake to determine the wakefulness level of the subject. With this technology, a scale is set for each subject by using, as a reference value, the heart rate and the blood pressure obtained when the subject is fully awake and applying the reference value to a previously set scale. Then, these values are applied to the scale every time the heart rate and the blood pressure of the subject are obtained, thereby determining a wakefulness level of the subject in real time.
Patent Document 1: International Publication Pamphlet No. WO 2008/65724
Patent Document 2: Japanese Laid-open Patent Publication No. 2006-34803
However, with the technologies described above, there is a problem in that it is difficult to determine the wakefulness level of a subject.
For example, with the conventional technology that uses heartbeat signals, in order to set the scale, there is a need to obtain both heartbeat signals obtained when a subject is fully awake and heartbeat signals obtained when the subject is not fully awake. However, in reality, it is difficult to obtain heartbeat signals when a subject is not fully awake. Consequently, setting the scale for each subject is not easy, and thus, in reality, determining a wakefulness level of the subject is difficult.
Furthermore, because the conventional technology that uses both heart rate and blood pressure does not use measured values that are obtained when a subject is not fully awake, the scale is set for each subject. However, because the biometric information that is used in this conventional technology is different from that used in the conventional technology that uses heartbeat signals, these technologies are not easily combined.